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Audio Note Ongaku
The 211 creates a formidable impression because of its shape. But the 211 may appear old-fashioned and unsophisticated to high-brow maniacs for audio equipment. Perhaps this is the reason why there are only a few amplifiers that employ the 211 tube today.
This type of amplifier is a challenge from the viewpoint of the manufacturer. The power supply circuit cannot be normally designed, since the supply voltage required for the 211 tube must be approximately 1000V. In manufacturing the amplifier, we must pay utmost attention to moisture-proofing the chassis and proper insulation of the wiring so as to prevent hands from getting electric shock if one reaches into the amplifier.
However, it is only large triodes like the 211 that provide the best performance that vacuum tubes can offer. The Eg-Ip characteristic of the 211 and its brothers is more linear than most other power tubes. Larger diameter wire is used for the heater, the grid to heater spacing is considerable, and coarse "pitch" is used for the grid winding geometry. This type of vacuum tube is very sturdy and promises a high vacuum integrity, since it was originally intended for demanding commercial and military applications.
When high plate voltage is employed and the pitch of the grid is made more coarse, the amount of "stray electrons" around the heater is greatly decreased, thereby allowing the vacuum tube to work in a more closely ideal manner. In particular, the large triode vacuum tube functions mare perfectly when dealing with low level signals, allowing the tone quality to be clear and distinct. If the design of the driver stage is satisfactory, the single triode power amplifier possesses an unbelievably law distortion characteristic, even in the absence of negative feedback. This fact demonstrates the excellent performance of this family of vacuum tubes.
Simple Is The Best
It is an interesting discovery that when mechanical sounds are thoroughly eliminated, we can reproduce live sound. What must we do to eliminate mechanical sound? First, we must simplify the audio circuitry. Next, we must carefully select the components which are used in the equipment.
At the closing stage of the vacuum tube amplifier age, tube circuit technology was in a highly advanced state. It was like the advanced evolution of dinosaurs at the close of the dinosaurian age. When I was only 20 years old, I concentrated my energies on the study of "negative feedback theory". At such an inexperienced age, one tends to concentrate on a meeting point, where theory seems to meet reality, instead of focusing on the sound itself. I still remember that I was trying to make up an ideal circuit so as to produce a good sound and my soldering iron was always in its heated state. In spite of my efforts, I could not go beyond the wall of "good" sounds. I finally arrived at the conclusion, after considerable trial and error, that the most important thing is to "make up an amplifier without depending on negative feedback." In fact, I found that I had to strive to simplify the circuitry even without negative feedback and also to develop my understanding of the characteristics of materials to be used and their effect on sound quality.
At one Audio Fair last year, we compared sound reproduced by a transistor amplifier produced by a famous manufacturer and sound reproduced by a 211 vacuum tube amplifier of apparent good quality. To my surprise, the 211 amplifier sounded exactly like the transistor amplifier! I expected more from the triode. Perhaps this was due to the use of feedback in the triode amplifier. Clearly to raise the performance of a single triode amplifier above the crowd it is necessary to optimize the design and parts quality used in its realization, It is not enough simply to use triodes.
I reemphasize that it is necessary to simplify the fabrication of an amplifier and to carefully select highest quality parts in order to reproduce a "quality of live sound" free from mechanical sound. These are the most important considerations in producing an ideal amplifier.
I Am An Enthusiast For Single-Ended Amplifiers
It is interesting that we cannot simply say "the single type can reproduce a good sound." Some single type amplifiers can produce more distortion. Choice of tube types is important in this respect. Distortion in the power tube cannot be eliminated completely, even if the previous stage is designed for minimum distortion. Push-pull circuits can eliminate the second harmonic produced in the output stage. This is the reason why many high class amplifiers employ the P-P configuration.
However, some say that a push-pull output stage makes the sound unclear. There is certainly a potential for unclear sound in these designs due to imbalances. The current state of parts, especially the OPT, is not sufficiently advanced to avoid this problem. The deterioration of sound quality due to improper balance is a challenge for the designer to solve 30 years from now. On this basis, the single type can be recommended, since this type is free from unclear sound due to imbalance.
However, there is a specific challenge which the single type must overcome and we cannot say that the single type is good unless it successfully overcomes this problem. In short, we cannot blindly become enthusiasts for single ended amplifiers.
Problem With Output Transformers
The world is as kind as it is cruel. The loss generated by the air gap brings the magnetic characteristics to a crisis (Note the hysteresis curve), thereby causing the smooth curve to be changed into a curve which is partially linear and gradually less and less linear as it approaches saturation. Actually, this action enhances the linearity of the mu (permeability) in the small signal region. The enhanced linearity in the low level signal range improves the transmission capability of small signals, thereby enabling greater clarity and detail in musical reproduction. This phenomenon does not occur in push-pull transformers.
Merely increasing the volume of the iron core, i.e. increasing the size of the sectional area of the iron core, will not necessarily lead to improvements in musical reproduction. There remains the problem of the tone quality reproduced by the material of the iron core. This is the reason why our company manufactures the OPTs at our own plant. Needless to say, we carefully select the material to be used for the iron core (by placing an importance on the resolution of sound) so as to reproduce good tone quality. Our transformer employs a cut core. A non-magnetizing band is used for the core as well as a non-magnetic transformer case. We pot our transformers with 24 hours-curing type epoxy to fix the coil and core securely to avoid mechanical resonances. The wire is wound around the bobbin by hand so as to provide a proper tension in the wire. No other OPT in the world is manufactured with such attention to the resulting quality of tone.
Matching Of The OPT And Power
This single triode amplifier displays outstanding low end characteristics when compared with other amplifiers of this type because the OPT core volume is very large. It can successfully reproduce a very soft and warm low-pitched sound. We tend to imagine that we can enhance the tone quality if we were to utilize high permeability core material. But permalloy has a weak point in that it cannot provide enough power in low notes, since it will saturate at a magnetic flux density below the operating point of power amplifiers. In order to reproduce good quality sound, we must carefully select the iron core material, carefully specify the winding method, and choose the material of the transformer wire with optimal sonic results in mind.
The largest problem with the tone quality of the condenser is a "noise between electrodes" - audible energy created by the above-mentioned resistance. Once this noise is produced, the electrode-to-electrode area will produce noise continuously. It adversely affects the tone quality because of its high Q resonance. The reproduced sound will become a metallic sound or a frivolous sound just like a rubbing sound produced by high-polymer films. The problem is part electrical and part mechanical.
The problem with condensers is not limited to crude forms of distortion. We are manufacturing condensers with particular emphasis on materials in order to minimize sonic deterioration. Specifically we use a thick silver-leaf for the electrode and wind the foil by hand making sure to provide enough tension. I still remember my deep emotion when I first listened to an amplifier using the silver-leaf condenser. The tone quality of this vacuum tube amplifier is so excellent that it is unparalleled in the world. The reproduced sound is, needless to say, free from metallic sound. A very dynamic sound effect and sound approaching live sound can be reproduced. The pizzicato of low strings can be reproduced properly in time. The reproduced sound really offers "music." Although the higher cost of the silver-leaf condenser is a disadvantage, the use of this type condenser is inevitable when the goal is to reproduce a really good sound. This must be a ‘favorite amusement of a king."
Circuit of The Ongaku Amplifier
Silver Wire Wound Output
Although they say that the resolution may be degraded if a signal is transmitted through the OPT, it is a well-known fact that the transformer can offer a good feeling of the music that the OTL cannot. Accordingly, we are required to solve the problem of how to enhance the resolution of sound with OPT.
I can still remember my deep emotion when I reproduced the sound using the MC step-up transformer wound with silver wire 13 years ago. Using silver, I could successfully resolve the "problem with the noise produced by the transformer," which we could not solve up to that time in the recording studio. From that time, we began using silver wire in a wider range of applications. We finally arrived at the conclusion that magnetism matches the silver wire better than the copper wire. The performance of the silver wire used in the magnetic circuit is wonderful. The performance gives us a feeling as if a signal which once got blocked rushes forward like floodwater. We can perceive that the signal flows smoothly without binding. The work of the silver wire is especially wonderful in the small signal area. The silver wire wound transformer contributes to the enhancement of tone quality reproduced by the vacuum tube amplifier, thereby allowing the vacuum tube amplifier to become famous for its good quality of reproduced sound. In some of our amplifiers, such as the KEGON/C, copper wire is used for the primary side of the OPT to reduce cost and only the secondary is wound with silver wire.
We must confess that it is not an easy task to master the secrets of the audio equipment!
Ongaku For The Rest Of Us
But wait... because Kondo-san was gracious enough to share his design with the international experimenter community. we can build our own 211 SE amps based on the Kondo masterpiece. Of course, we can't build a real Ongaku -- part of the celebrated sonic magic of the amp is in its exquisite material execution and the special virtues of in-house Audio Note parts. But I'll bet the Kondo circuit will turn in a respectable performance even when more pedestrian materials are employed. Until the Sound Practices publishing empire hits the "big time", I'm afraid I must settle for second best when a savings of $60,000 is involved.
Some interesting components are available from Audio Note, UK which would be appropriate for a "Poor Man's Ongaku" project. including single ended transformers for the 211 and a line of oil/paper coupling caps. A primary mission of the Audio Note UK operation is to make some of the findings, of Kondo's uncompromising explorations available to the audiophile who isn't blessed with an Ongaku-sized budget. Toward this goal, they are developing a line of lesser-priced equipment of high musical achievement along with providing a selection of music quality parts for fellow audio adventurers.
OK, homebrewers... time to get those soldering irons "in the heated state", as Kondo-san puts it. Next time: my report on "Building the Poor Man's Ongaku" and more on this interesting design.